The present invention relates to developer compositions and, in particular, to liquid developers containing novel charge control agents. In embodiments, the present invention relates to liquid developers comprising acid aluminum salt charge control agents such as aluminum salts of acids, especially hydroxy carboxylic acids, amino carboxylic acids, sulfonic acids, aliphatic carboxylic acids, and aromatic carboxylic acids.
The developers of the present invention can be selected for a number of known imaging and printing systems, such as xerographic processes, wherein latent images are rendered visible with the liquid developer illustrated herein. The image quality, solid area coverage and resolution for developed images usually require sufficient toner particle electrophoretic mobility. The mobility for effective image development is primarily dependent on the imaging system used. The electrophoretic mobility is primarily directly proportional to the charge on the toner particles and inversely proportional to the viscosity of the liquid developer fluid. A 10 to 30 percent change in fluid viscosity caused, for instance, by a 5.degree. to 15.degree. C. decrease in temperature could result in a decrease in image quality, poor image development and background development, for example, because of a 5 percent to 23 percent decrease in electrophoretic mobility. Insufficient particle charge can also result in poor transfer of the toner to paper or other final substrates. Poor or unacceptable transfer can result in, for example, poor solid area coverage if insufficient toner is transferred to the final substrate and can also lead to image defects such as smears and hollowed fine features. To overcome or minimize such problems, the liquid toners of the present invention were arrived at after extensive research efforts, and which toners result in, for example, sufficient particle charge for transfer and maintain the mobility within the desired range of the particular imaging system employed. Advantages associated with the present invention include increasing the desired negative charge on the developer particles and in embodiments providing a charge adjuvant, also referred to as a charge additive, charge agent, charge control agent, or charge enhancer, that is superior to other charge adjuvants, such as aluminum stearate. The superior charge can result in improved image development and superior image transfer.
A latent electrostatic image can be developed with toner particles dispersed in an insulating nonpolar liquid. The aforementioned dispersed materials are known as liquid toners or liquid developers. A latent electrostatic image may be produced by providing a photoconductive layer with a uniform electrostatic charge and subsequently discharging the electrostatic charge by exposing it to a modulated beam of radiant energy. Other methods are also known for forming latent electrostatic images such as, for example, providing a carrier with a dielectric surface and transferring a preformed electrostatic charge to the surface. After the latent image has been formed, it is developed by colored toner particles dispersed in a nonpolar liquid. The image may then be transferred to a receiver sheet or supporting substrate.
Useful liquid developers can comprise a thermoplastic resin and a dispersant nonpolar liquid. Generally, a suitable colorant, such as a dye or pigment, is also present. The colored toner particles are dispersed in a nonpolar liquid which generally has a high volume resistivity in excess of 10.sup.9 ohm-centimeters, a low dielectric constant, for example below 3.0, and a high vapor pressure. Generally, the toner particles are less than 30 micrometers average by area size as measured using the Malvern 3600E particle sizer.
Since the formation of proper images depends, for example, on the difference of the charge between the toner particles in the liquid developer and the latent electrostatic image to be developed, it has been found desirable to add a charge director compound and charge adjuvants which increase the magnitude of the charge, such as polyhydroxy compounds, amino alcohols, polybutylene succinimide compounds, aromatic hydrocarbons, metallic soaps, and the like to the liquid developer comprising the thermoplastic resin, the nonpolar liquid and the colorant.
U.S. Pat. Nos. 5,223,368 and 5,324,613, both to Ciccarelli et al, the disclosures of which are totally incorporated by reference herein in their entireties, disclose negatively charged dry toners containing resin, pigment and an aluminum hydroxide charge additive, or the hydrates thereof, and developer compositions with the aforementioned toner and imaging processes thereof. Aluminum salts of alkylated salicylic acid, such as hydroxy bis 3,5-tertiary butyl salicylic! aluminate are disclosed as charge control agents.
U.S. Pat. No. 5,308,731 discloses a liquid developer comprised of a liquid, thermoplastic resin particles, a nonpolar liquid soluble charge director, and a charge adjuvant comprised of metal hydroxy acid complexes such as aluminum hydroxycarboxylic acids, and more specifically, aluminum salicylate, as charge adjuvants. The disclosure of this patent is herein incorporated by reference in its entirety.
Illustrated in U.S. Pat. No. 5,306,591 is a liquid developer comprised of a liquid component, thermoplastic resin, an ionic or zwitterionic charge director, or directors soluble in a nonpolar liquid; and a charge additive, or charge adjuvant comprised of an imine bisquinone. Illustrated in U.S. Stat. Inv. Reg. No. H1483 is a liquid developer comprised of thermoplastic resin particles, and a charge director comprised of an ammonium diblock copolymer.
In U.S. Pat. No.5,366,840, there is disclosed a liquid developer comprised of thermoplastic resin particles, an optional charge director, and a charge additive comprised of aluminum-di-tertiary-butyl salicylate or ALOHOS. The disclosure of this reference is hereby incorporated by reference in its entirety.
U.S. Pat. No. 5,019,477 to Felder, the disclosure of which is hereby incorporated by reference in its entirety, discloses a liquid electrostatic developer comprising a nonpolar liquid, thermoplastic resin particles, and a charge director. The ionic or zwitterionic charge directors may include both negative charge directors such as lecithin, oil-soluble petroleum sulfonate and succinimide, and positive charge directors such as cobalt and iron naphthanates. The thermoplastic resin particles can comprise a mixture of (1) a polyethylene heteropolymer or a copolymer of (i) polyethylene and (ii) acrylic acid, methacrylic acid or alkyl esters thereof, wherein (ii) comprises 0.1 to 20 weight percent of the copolymer; and (2) a random copolymer of (iii) selected from the group consisting of vinyl toluene and styrene and (iv) selected from the group consisting of butadiene and acrylate. As the copolymer of polyethylene and methacrylic acid or methacrylic acid alkyl esters, NUCREL.sup.R may be selected.
U.S. Pat. No. 5,030,535 to Drappel et al. discloses a liquid developer composition comprising a liquid vehicle, a charge control additive and toner particles. The toner particles may contain pigment particles and a resin selected from the group consisting of polyolefins, halogenated polyolefins and mixtures thereof. The liquid developers are prepared by first dissolving the polymer resin in a liquid vehicle by heating at temperatures of from about 80.degree. C. to about 120.degree. C., adding pigment to the hot polymer solution and attriting the mixture, and then cooling the mixture so that the polymer becomes insoluble in the liquid vehicle, thus forming an insoluble resin layer around the pigment particles.
U.S. Pat. Nos. 3,852,208 and 3,933,664, both to Nagashima et al., disclose colored, light-transparent photoconductive material which is obtained by a condensation reaction of organic photoconductive substances with reactive colored components. The chemical combination of an organic photoconductive substance having at least one amino or hydroxyl group with a color development component having at least one active halogen atom produces the color developing organic photoconductive materials. Alternatively, the color developing materials can be obtained from the combination of an organic photoconductive substance having at least one active halogen atom with a color developing component having at least one amino or hydroxyl group. The color developing organic photoconductive material may be pulverized in a ballmill, a roll-mill or an atomizer to produce a toner for use as a dry or wet developing agent, or may be used in combination with other colored substances or vehicle resins.
U.S. Pat. No. 4,524,119 to Luly et al. discloses electrophotographic dry development carriers for use with toner particles wherein the carrier core particles are coated with fluorinated carbon or a fluorinated carbon-containing resin. By varying the fluorine content of the fluorinated carbon, systematic uniform variation of the resistivity properties of the carrier is permitted. Suitable binders for use with the carrier core particles may be selected from known thermoplastics, including fluoropolymers.
U.S. Pat. No. 5,026,621 to Tsubuko et al. discloses a toner for electrophotography which comprises as main components a coloring component and a binder resin which is a block copolymer comprising a functional segment (A) consisting of at least one of a fluoroalkylacryl ester block unit or a fluoroalkyl methacryl ester block unit, and a compatible segment (B) consisting of a fluorine-free vinyl or olefin monomer block unit. The functional segment of block copolymer is oriented to the surface of the block polymer and the compatible segment thereof is oriented to be compatible with other resins and a coloring agent contained in the toner, so that the toner is provided with both liquid repelling and solvent soluble properties.
U.S. Pat. No. 4,248,954 to Datta et al. discloses carrier particles for use with a dry toner composition in an electrophotographic process, which are prepared by coating the surface of the carrier particles with a perfluorocarboxylic acid in a polymeric binder. The carrier particles are capable of imparting a positive triboelectric charge to toners used with these carrier particles.
U.S. Pat. No. 4,268,598 to Leseman et al. discloses a developing powder composition prepared by blending a fluoroaliphatic sulfonamido surface active agent with a desired formulation of toner powder particles. The toner powders are flowable, fimely divided dry powder that are generally colored and are preferably conductive and magnetically attractable.
U.S. Pat. No. 4,139,483 to Williams et al. discloses a finely divided dry toner composition comprising a colorant, a thermoplastic resin, and a surface active additive which is capable of providing a desired polarity and magnitude of triboclectric charging potential to the toner composition. The surface active additives are selected from highly fluorinated materials.
U.S. Pat. No. 4,113,641 to Brana et al. discloses a dry development powder with a high charge to mass ratio comprising a carrier particle treated with a perfluoroalkyl sulfonic acid. The core of the carrier particle is any material which can react chemically with perfluoro sulfonic acid, and is preferably a ferromagnetic material such as iron or steel.
U.S. Pat. No. 4,388,396 to Nishibayashi et al. discloses developer particles comprising pigment particles, a binder and an offset-preventing agent selected from the group consisting of aliphatic fluorocarbon compounds and fluorochlorocarbon compounds. Electrical conductivity can be imparted to the developer by causing electrically conductive fine particles to adhere to the surfaces of the particles.
U.S. Pat. No. 4,468,446 to Mikami et al. discloses a dry electrostatographic toner for a pressure fixing process which comprises encapsulated toner particles with a pressure fixable adhesive core material containing a colorant and a pressure rupturable shell enclosing the core material, wherein the outer surface of the shell is an organofluoro compound.
Moreover, in U.S. Pat. No. 4,707,429 there are illustrated, for example, liquid developers with an aluminum stearate charge additive. Liquid developers with charge directors are also illustrated in U.S. Pat. No. 5,045,425. Further, stain elimination in consecutive colored liquid toners is illustrated in U.S. Pat. No. 5,069,995. Additionally, of interest are U.S. Pat. Nos. 4,760,009; 5,034,299 and 5,028,508.
In pending U.S. application Ser. No. 986,316, the disclosure of which is hereby incorporated herein by reference in its entirety, there is illustrated a process for forming images which comprises (a) generating an electrostatic latent image; (b) contacting the latent image with a developer comprising a colorant and a substantial amount of a vehicle with a melting point of at least about 25.degree. C., said developer having a melting point of at least about 25.degree. C., aid contact occurring while the developer is maintained at a temperature at or above its melting point, said developer having a viscosity of no more than about 500 centipoise and a resistivity of no less than about 10.sup.8 ohm-cm at the temperature maintained while the developer is in contact with the latent image; and (c) cooling the developed image to a temperature below its melting point subsequent to development.
The disclosures of each of the U.S. patents just mentioned are incorporated herein by reference in their entirety.